Hi. Yes I am thinking of boric acid! Borax apparently is available in the uk but its sale is restricted. It is mostly used as a cleaning product and to kill small critturs like ants! Soap kitchen advertise it for sale but I can't get their website to work so I don't know any more about it.
Trying to recall my coffee soap recipe (I am not at home) base recipe - 210 coconut oil, 300 olive oil 30 each shea butter, cocoa butter and castor oil , plus extra 75 coconut oil ( I think - because of the salt), 15 coffee grounds (I actually make the coffee with the water for the lye and leave the grounds in - let it cool first!), 75 sea salt and 30 pumice powder - all in grams. Lye I think 86 g, water at 1.5 x the lye. But if you run the base recipe, without anything after the plus, through a
soap calculator that will give the lye amount. Always check other peoples recipes.
It was very cleansing, not for use on the face. I used to call "working hands" soap. Included coffee, salt and pumice with the idea that it was a combination cooks, gardeners and anything else mucky you could think of soap. Someone who worked on a farm used to buy lots of it.